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SodaLive/Sources/FortuneWheel/FortuneWheelViewModel.swift

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+//
+//  FortuneWheelViewModel.swift
+//  SodaLive
+//
+//  Created by klaus on 2023/12/07.
+//
+
+import SwiftUI
+
+class FortuneWheelViewModel: ObservableObject {
+
+    private var pendingRequestWorkItem: DispatchWorkItem?
+    @Published var degree = 0.0
+
+    private let model: FortuneWheelModel
+
+    init(model: FortuneWheelModel) {
+        self.model = model
+    }
+
+    private func getWheelStopDegree() -> Double {
+        var index = -1;
+        if let method = model.getWheelItemIndex { index = method() }
+        if index < 0 || index >= model.titles.count { index = Int.random(in: 0..<model.titles.count) }
+        index = model.titles.count - index - 1;
+        /*
+         itemRange - Each items degree range (For 4, each will have 360 / 4 = 90 degrees)
+         indexDegree - No. of 90 degrees to reach i item
+         freeRange - Flexible degree in the item, so the pointer doesn't always point start of the item
+         freeSpins - No. of spins before it goes to selected item index
+         finalDegree - Final exact degree to spin and stop in the index
+         */
+        let itemRange = 360 / model.titles.count;
+        let indexDegree = itemRange * index;
+        let freeRange = Int.random(in: 0...itemRange);
+        let freeSpins = (2...20).map({ return $0 * 360 }).randomElement()!
+        let finalDegree = freeSpins + indexDegree + freeRange;
+        return Double(finalDegree);
+    }
+    
+    func spinWheel() {
+        withAnimation(model.animation) {
+            self.degree = Double(360 * Int(self.degree / 360)) + getWheelStopDegree();
+        }
+        // Cancel the currently pending item
+        pendingRequestWorkItem?.cancel()
+        // Wrap our request in a work item
+        let requestWorkItem = DispatchWorkItem { [weak self] in
+            guard let self = self else { return }
+            let count = self.model.titles.count
+            let distance = self.degree.truncatingRemainder(dividingBy: 360)
+            let pointer = floor(distance / (360 / Double(count)))
+            if let onSpinEnd = self.model.onSpinEnd { onSpinEnd(count - Int(pointer) - 1) }
+        }
+        // Save the new work item and execute it after duration
+        pendingRequestWorkItem = requestWorkItem
+        DispatchQueue.main.asyncAfter(deadline: .now() + model.animDuration + 1, execute: requestWorkItem)
+    }
+}